1. Field of the Invention
Embodiments of the invention described herein pertain to the field of horizontal surface pumps. More particularly, but not by way of limitation, one or more embodiments of the invention enable an apparatus and system for a thrust-absorbing horizontal surface pump assembly.
2. Description of the Related Art
Submersible pump assemblies are typically used to artificially lift fluid to the surface in deep wells such as oil, water or gas wells. Additionally, in some instances, fluids must be pressurized and moved between surface locations and/or transported through a supply line to a tank. For example, it may be desirable to transport produced oil to a processing facility located remotely from the well. In such circumstances, submersible pumps may be used as surface pumps in horizontal pumping systems. Horizontal surface pump assemblies are also used for salt water disposal, water injection and other fluid transfer applications. Horizontal pumping assemblies typically include a multistage centrifugal pump horizontally mounted to a skid and driven by an electric motor, the pump assembly components are connected together by rotating shafts. The electric motor turns the shafts, which operates the pump. Horizontal pumps operate at rotational speeds of between 1800 and 3600 RPM, which requires the pump to be capable of bearing high axial loads, for example ranging from about 4,000 to 6,000 pounds in systems making use of roller element bearings.
To handle the thrust of the pump, a standalone thrust chamber is conventionally placed in between the motor and the intake of the horizontal pump assembly. Thrust bearings in the thrust chamber are submerged in a cavity of clean motor oil, carrying the thrust of the pump and maintaining shaft alignment. A conventional horizontal surface pump assembly including a standalone, motor-oil cooled thrust chamber is illustrated in FIG. 1. As shown in FIG. 1, conventional standalone thrust chamber 1 is between conventional surface motor 2 and conventional intake 6 of conventional pump 3.
In thrust chambers of horizontal surface pumps, such as conventional standalone thrust chamber 1, hydrodynamic bearings and roller element bearings are the most commonly implemented thrust bearings. However, roller element bearings are not well suited for horizontal surface pump applications because they wear out too quickly due to the high rotational speeds and loads to which the horizontal pumps are subjected, and they generate too much heat due to oil sheer.
Conventional hydrodynamic bearings also suffer from drawbacks. One drawback is that conventional bearings often do not include sufficient surface area to carry the loads required of horizontal surface pumps. The rotating disk of a hydrodynamic thrust bearing is typically a hard material such as tungsten carbide. The stationary disk typically includes softer metal pads made of bronze. However, bronze is only capable of carrying a load of about 500 pounds per square inch. There is often insufficient space to include large enough copper pads on the stationary disk to carry the required loads.
Another significant drawback to conventional hydrodynamic bearings is that conventional hydrodynamic bearings cannot withstand contamination (e.g., by dirt) of the motor oil in the thrust chamber. As a result, conventional hydrodynamic bearings must be placed in a cavity of clean motor oil, which is located in conventional thrust chamber 1 of a horizontal surface pump assembly. However, contamination of the cavity of clean motor oil is a common occurrence due to typical oil field or other operating conditions. Thus, motor oil-cooled thrust chambers, such as conventional thrust chamber 1, require regular maintenance such as oil changes. In addition, if a bearing failure occurs, for example due to contaminated motor oil in the chamber, the entire thrust chamber of a conventional horizontal pump assembly must be replaced, which is time consuming and expensive.
A conventional hydrodynamic bearing includes two round disks. One disk is fixed, while the other is turned by the shaft in rotation about the central axis of the fixed disk. A conventional fixed disk of the prior art is illustrated in FIGS. 2A and 2B. In some approaches, as illustrated in FIGS. 2A and 2B, the conventional fixed disk is designed with conventional copper pads. The flat, rotating disk pulls motor oil between the conventional pads. As long as there is clean motor oil between the surfaces, the thin film of fluid creates separation between the disks with hydrodynamic lift. On a conventional rotating disk, a solid surface is required on which the conventional pads rotate. Each pad deflects ever so slightly such that a wedge is formed at the leading edge. The leading edge is convergent, the trailing edge is divergent. The wedge produces a hydrodynamic profile that provides lift. The conventional pads and rotating disk must never make contact with each other or a catastrophic failure will occur. As a result, extreme pressure additives are added to the motor oil in the standalone thrust chamber. Additives provide a boundary layer of protection to prevent direct face contact until a wedge is formed. To function properly, the surfaces of hydrodynamic bearings must be flat and smooth. A typical hydrodynamic thrust bearing is usually designed to operate with a fluid thickness of between about 0.001 and 0.0004 inches. Any impurities that are thicker than the oil film between the disks, such as the common occurrence of dirt in the motor oil, can cause surface damage to the bearings. Resulting friction between the disks reduces or eliminates their hydrodynamic properties.
Thus, conventional horizontal surface pumps are not well suited to carry thrust under typical operating conditions and are expensive and time consuming to maintain and repair. Therefore, there is a need for an apparatus and system for a thrust-absorbing horizontal surface pump assembly.